1. Field of the Invention
The present invention generally relates to a lubricator assembly employed at a well head of a gas-producing well and, more particularly, is concerned with a well head lubricator assembly employing a polyurethane impact-absorbing spring.
2. Description of the Prior Art
Gas-producing wells typically employ a gas lift plunger disposed within the tubing of a well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner well-known to one of ordinary skill in the art. The plunger is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface or well head while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug, of liquid has been delivered to the surface and the pressure of gas flowing from the well tubing has decreased below the force of gravity on the plunger.
Such gas-producing wells also typically employ a lubricator assembly mounted at the well head in communication with the upper end of the well tubing. The various functions of the lubricator assembly are to (1) catch the plunger when it arrives at the well head, (2) externally mount a sensor which detects the arrival of the plunger at the lubricator and sends a signal to an electronic controller at the well head, and (3) permit easy access to the plunger when required for maintenance purposes.
Heretofore, as seen in FIGS. 1 and 2, one conventional lubricator assembly, generally designated 10, has included an elongated rigid tubular body 12 defining an interior chamber 14 of a substantially cylindrical configuration, an end cap 16 removably mounted on and closing an upper end portion 12a of the tubular body 12, a strike plate 18 disposed in the interior chamber 14 at a lower end portion 12b of the tubular body 12, and an elongated coil spring 20 disposed in the interior chamber 14 of the tubular body 12 between the upper end cap 16 and lower strike plate 18. The coil spring 20 is made of a suitable metal, such as conventional steel, and is intended to function to absorb the high impact forces generated by the leading end of the arriving plunger on the strike plate 18 and thereby protect the rest of the structure of the lubricator assembly 10.
Under certain operating conditions and for various reasons, the problem of premature collapse and failure of the conventional steel coil spring 20 has been experienced, in some cases in a relatively short period of time. The collapse and failure of the steel coil spring 20 allows the plunger to hit substantially with full force against the end cap 16 on the tubular body 12 of the lubricator assembly 10, causing the plunger to break up and get stuck in the tubular body 12 which requires a shutdown of the well to make the necessary repair and/or replacement of damaged components.
Consequently, a need exists for an innovation in the construction of the lubricator assembly employed at the well head of a gas-producing well which will provide a solution to the aforementioned problem without introducing any new problems in place thereof.
The present invention provides an improved lubricator assembly designed to satisfy the aforementioned need. The improved lubricator assembly of the present invention employs a polyurethane spring which will withstand the impact forces generated by extremely high plunger speeds without failure compared to the conventional metal, namely steel, coil spring which will collapse and fail under the same conditions. In testing the polyurethane spring versus the conventional steel coil spring, the steel coil spring failed within three days whereas the polyurethane spring after sixty days was still in excellent condition.
Accordingly, the present invention is directed to a well head lubricator assembly which comprises: (a) an elongated rigid tubular body having an upper end and a lower end and defining an interior chamber open at the lower end of the tubular body for receiving a leading end of a plunger at a well head, the tubular body having an end structure thereon closing the interior chamber at the upper end of the tubular body; and (b) an elongated body made substantially of a polyurethane material and having a longitudinal axis and characteristics of a coil spring in that the elongated body is capable of resiliently compressing along the longitudinal axis and of springing back to substantially an original form of the elongated body, the elongated body being disposed in the interior chamber of the tubular body between the end structure and the lower end of the tubular body such that upon arrival of the plunger at the tubular body the elongated body will be impacted by the force of the plunger and absorb the impact force.
The present invention also is directed to an impact-absorbing spring which comprises: (a) an elongated body made substantially of a polyurethane material and having a longitudinal axis; (b) the elongated body also having the characteristics of a coil spring in that the elongated body is capable of resiliently compressing along the longitudinal axis thereof and of springing back substantially to an original form.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.